Current sensor for low pass filter

ABSTRACT

A sense winding is included as part of a current sensor which senses the output current of a low pass filter utilized in a high current power supply system. The sense winding is provided with an equivalent number of turns as the filter&#39;&#39;s inductor has and is magnetically coupled to it in a voltage cancelling relationship. The current sensor provides a sense output signal which is proportional to the filter&#39;&#39;s output current and derived substantially from the voltage drop across the effective DC resistance of the inductor.

I United States Patent 11 1 1111 3,733,536 Gillow et al. [4 1 May 15, 1973 54] CURRENT SENSOR FOR LOW PASS 2,308,013 1 1943 Lee ..321 10 x FILT R 2,356,617 8/1944 Rich 2,954,523 9/1960 Rosenstock ..324/l27 X [75] Inventors: Albert V. Glllow, Berkshire; Wendell Marple, Vestal, both of N Primary Examiner-James D. Trammell [73] Assignee: International Business Machines Atwmey Norman Bardales et Corporation, Armonk, N.Y. ABSTRACT {22] Flled: June 1972 A sense winding is included as part of a current sensor [21] Appl. No.: 259,938 which senses the output current of a low pass filter utilized in a high current power supply system. The sense winding is provided with an equivalent number [52] U.S. Cl ..32l/l0, 324/127 of turns as the filter,S inductor has and is magnetically Cl. coupled to in a voltage li g relationship. The [58] Field of Search ..321/l0; 324/126, current Sensor provides a sense output Signal which is 324/127 128; 328/162 1651 167; 317/53 proportional to the filter's output current and derived substantially from the voltage drop across the effective [56] ef e e Cited DC resistance of the inductor.

UNITED STATES PATENTS 5 Claims, 2 Drawing Figures 1,733,232 10/1929 Miessner ..32l/l0 X -i2 5 i0 7 5 "1 i 11 -2 6 PATENTKE' 1 5 3 .FIG.

FIG.

1 CURRENT SENSOR FOR LOW PASS FILTER BACKGROUND OF THE INVENTION l. Field of the Invention This invention is related to current sensors for low pass filters used in high current power supply systems.

2. Description of the Prior Art High current power supply systems employing a low pass filter are well known in the art. Because of the high current utilized, an appreciable power loss results across the filter inductor due to the presence of the effective DC resistance of the inductor.

In certain cases, it is desirous to provide a current sensor to sense the current passing through the inductor and hence through the load. Heretofore in the prior art, this was accomplished by providing a discrete, i.e. external, resistance in series with the filter inductor and measuring the voltage thereacross. The current passing through the discrete resistance was thus proportional to the current in the filter inductor and/or load. However, this arrangement further increased the power losses to the load due to the presence of the aforementioned external resistance.

SUMMARY OF THE INVENTION It is an object of this invention to mitigate the power losses in a high current power supply system employing a low pass filter and current sensor.

It is another object of this invention to provide in combination a current sensor and low pass filter in a high current power supply system in which the current sensor coacts with the effective DC resistance of the filter inductor to provide a sense signal which is proportional to the filters output Current.

Accordingly, it is a feature of this invention to provide in a high current power supply system, circuit apparatus comprising in combination low pass filter means which has an inductor with a predetermined number of turns and a capacitor serially connected to the inductor. In addition, current sensor circuit means for sensing the filters output current is provided and comprises a sense winding which has a'number of turns equivalent to the predetermined number of turns of the inductor. The sense winding is magnetically coupled to the filter inductor in a voltage cancelling relationship. The current sensor has sense signal output means which provides a sense signal proportional to the filters output current and derived substantially from the voltage drop across the effective resistance of the inductor.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of the preferred embodiment of the invention, as illustrated in the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a schematic view ofa preferred circuit apparatus embodiment of the invention and FIG. 2 is the equivalent circuit diagram of the circuit apparatus of FIG. 1.

In the figures, like elementsare designated with similar reference numerals.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. I, inductor 1 and capacitor 2 coact as a low pass filter in a high current power supply system. By way of example the input terminals 3, 4 are adapted to be coupled to a source, not shown, of recurring unipolar pulses, e.g. pulse 5 of the idealized waveform partially shown, having a periodicity T and width W. For sake of clarity, the load 6 is shown in dash line form and is connected across the output terminals 7 and 8. As shown, the low pass filter has its inductor 1 in series coupling relationship with the load 6; whereas, the low pass filters capacitor 2 is connected in parallel coupling relationship with the load 6.

In accordance with the principles of the present invention, current sensor means is provided to sense the filters output current which is substantially the current I1 passing through the inductor 1. More specifically, a sense winding 9, which has an equivalent number of turns as is provided for the filters inductor l, is magnetically coupled to the inductor l in a voltage cancelling relationship as indicated by the conventional dot polarity shown in FIG. 1. The sense winding 9 is shunted across the inductor l by virtue of their respective connections to the node 10. The current sensor is provided with current sense output means shown as terminals 11 and 7, the later terminal being common to the current sensor and filter outputs. In the preferred embodiment, the sense winding 9 and the inductor l are wound on a common core 12 The operation of the apparatus of FIG. 1 will now be described in conjunction with its equivalent circuit diagram shown in FIG. 2. The low pass filter l, 2 converts the unipolar input pulses present at its input terminals 3, 4 to a DC voltage at the output terminals 7, 8 in a manner well known to those skilled in the art. The filter circuit parameters such as the impedances of the induc-. tor l and capacitor 2, as well as the input signal parameters such as pulse amplitude, width, and frequency, govern the DC level and/or ripple content of the DC output voltage.

For purposes of explanation, the inductor 1 of FIG. 1 is represented in FIG. 2 by its inductive and effective DC resistance components la and lb, respectively. Likewise, the sense winding 9 of FIG. 1 is represented in FIG. 2 by its inductive and effective DC resistance components 9a and 9b, respectively. The impedances Z1 and Zs, shown schematically in FIG. 2, represent the load impedance and impedance of the measuring instrument circuit, it being understood that Zs Zl.

In accordance with well known circuit theory, the instantaneous voltage loop equation around the loop comprising inductor 1, sense winding 9 and the the measuring instrument circuit Zs is given by the following equation:

0=Vx+Vl Vy- V2 Vs.

since |Vx|=l Vyl, equation (I) may be written as follows:

Since the impedance Zs is generally much greater than the effective DC resistance 9b, equation (2) may be reduced, as follows:

where 11 the output filter current Rlb the resistance value of the effective DC resistance of inductor 1. The output filter current ll is related to the measuring circuit current l2 and filter input current Iin, as follows;

lin=ll +12 TABLE 1 Capacitor 2 2000 ufarads Inductor l:

inductance l5 thenrys effective DC resistance 0.0035 ohms no. of turns AWG SIZE No. 12 Sense winding 9:

inductance l5 uhenrys effective DC resistance 0.23 ohms No. of turns 10 AWG SlZE No. 30

Input parameters:

pulse amplitude pulse frequency ulse width Filter utput parameters:

C level 15 volts, peak 33 kilohertz l0 usec.

5 volts DC to 50 amps 70 to 175 millivolts output current Sensor Voltage (Vs) Measuring instrument circuit impedance 100 ohms It should be understood that while the invention has been particularly shown and described with reference toa preferred embodiment, it will be understood by those skilled in theart that the foregoing and other changes in form and detail may be made therein without departing from the spirit and scope of the invention.

We claim:

1. In a high current power supply system, circuit apparatus comprising in combination:

low pass filter means having an inductor with a predetermined first number of turns and a capacitor serially connected thereto, said filter providing an output current; and

current sensor means comprising sense signal output means and a sense winding having a second number of turns equivalent to said predetermined first number, said winding being magnetically coupled to said inductor in a voltage cancelling relationship, said current sensor means providing a sense signal at said sense signal output means proportional to the filters said output current and derived substantially from the voltage drop across the effective DC resistance of the inductor.

2. Circuit apparatus according to claim 1 wherein said low pass filter means further comprises filter output means in series and parallel coupling relationships with said inductor and capacitor, respectively.

3. Circuit apparatus according to claim 1 wherein said sense winding is also electrically connected to said inductor.

4. Circuit apparatus according to claim 1 wherein said inductor and said sense winding are wound on a core member.

5. Circuit apparatus according to claim 1 wherein said inductor is formed of a wire conductor of a predetermined first diameter size, and said sense winding is formed of another wire conductor of a predetermined smaller second diameter size. 

1. In a high current power supply system, circuit apparatus comprising in combination: low pass filter means having an inductor with a predetermined first number of turns and a capacitor serially connected thereto, said filter providing an output current; and current sensor means comprising sense signal output means and a sense winding having a second number of turns equivalent to said predetermined first number, said winding being magnetically coupled to said inductor in a voltage cancelling relationship, said current sensor means providing a sense signal at said sense signal output means proportional to the filter''s said output current and derived substantially from the voltage drop across the effective DC resistance of the inductor.
 2. Circuit apparatus according to claim 1 wherein said low pass filter means further comprises filter output means in series and parallel coupling relationships with said inductor and capacitor, respectively.
 3. Circuit apparatus according to claim 1 wherein said sense winding is also electrically connected to said inductor.
 4. Circuit apparatus according to claim 1 wherein said inductor and said sense winding are wound on a core member.
 5. Circuit apparatus according to claim 1 wherein said inductor is formed of a wire conductor of a predetermined first diameter size, and said sense winding is formed of another wire conductor of a predetermined smaller second diameter size. 